Bananarama! Vibration!!!!!

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drewcrane
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Post by drewcrane »

[quote="GJUK"]How can the prop angle make such a huge change?
(serious question)[/quote

The angle counter acts the other angle, acting as a cancellation, resulting in no vibration,if they are even with each other as they spin faster a harmonic will develop resulting in a vibration at certain speeds,now this is the laymen s explanation and I understand it

,but I too messed with the angle I even bought some angle wedges designed for lifted trucks I have that thing tilted 3 degrees and I couldn't even make it down the street, I did find most of my vibration it was the wilwood rear brakes the hub was just slightly to big ,and even with it vibes like an earth quake. and I also had an aluminum drive shaft made,and that helped a bit I went though u joints, cut the old drive shaft to see in side and there was a pretty decent dent in on the inside damper, so it was alot of little things including tires,I had them balanced and drove on them for 500 miles and had them check again and sure enough they were out of balance again

The car still has a slight vibration ,in the seat but I just gave up and at least I can see out the rear view mirror :thumbright:
GJUK
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Post by GJUK »

Interesting.

So for example if your gearbox was pointing to the ground by 2 degrees, the prop would have to meet the diff, which was pointing up by 2 degrees?
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drewcrane
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Post by drewcrane »

GJUK wrote:Interesting.

So for example if your gearbox was pointing to the ground by 2 degrees, the prop would have to meet the diff, which was pointing up by 2 degrees?
Yea or the other way around, as long as there is the same angle present.

Again I am no expert,as a matter of fact that is how I met Dave R he had his forum and my bro Buzz found it and from then on I have tried alot of different things I have found on boards.

My car I am convinced my vibration is a body vibration,

two parts of steel slapping each other ,mostly in the floor,I cant do anything else off the car I even used a frame alignment tool and found the right front was higher than the rest of the car,

due to the previous owner going jethro and launching it off a curb.

These cars are old and have been through alot, and who knows what some did back in the 70,s :roll:
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db
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Post by db »

I found this helpful, especially as mine's non-standard (4-link)
I also found a digital magnetic spirit level was superb for jobs like this.
Ignore the circles- they're for my set-up!
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Dave-R
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Post by Dave-R »

UJs work best at a slight angle.

Every rotation makes each UJ on the driveshaft rotate at the same speed.

The greater the angle in a UJ the further it has to swing in each rotation. So the faster it has to swing.

When they are at the same angle at each end of the driveshaft they are swinging at the same speed as each other. They are at the same frequency but out of phase by 180 degrees. So the frequencies they produce cancel each other out.

If one UJ is at a different angle to the other they have different frequencies.

When two different frequencies travel together you get some bits that are cancelled out as before but also other bits where the amplitude (height of the wave) is added together.

So now you have these spikes of vibration moving along the driveshaft with rpm.

Hope that is understandable.
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Post by GJUK »

Should be a Sticky! Very interesting thank you.
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Dave-R
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Post by Dave-R »

Actually I just made that up.

But there is a chance it is right. :D
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Post by MilesnMiles »

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Dave-R
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Post by Dave-R »

MilesnMiles wrote:Chapter and verse PDF here;

http://www.iedls.com/asp/admin/getFile. ... =28&FN=PDF
Good link! :thumbright:
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Post by db »

Great info Miles :thumbright:
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Post by MilesnMiles »

Yes, I was most impressed as I have some vibe issues to address too.
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drewcrane
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Post by drewcrane »

MilesnMiles wrote:Chapter and verse PDF here;

http://www.iedls.com/asp/admin/getFile. ... =28&FN=PDF
Very nice Book marked :thumbright:
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sinny
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Post by sinny »

Much to my frustration the vibration saga continues!!! :shock:

I've replaced the trans bush & adjusted the angles so the trans is pointing up 2.5 degrees & the diff down 2.5 degrees but no joy!

Today I pulled the half shafts out & ran it on jack stands & the vibration was still there! But it's not the with the drive shaft removed. I've changed the driveshaft for a 2nd hand one but no joy.

My thoughts are now that both propshafts I've tried are out of balance but is there anything else anyone can think of?
Last edited by sinny on Tue Apr 14, 15 7:00 pm, edited 1 time in total.
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Pete
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Post by Pete »

I take it you changed the Pig for a different ratio one as well?

If you had pulled the half shafts and it still vibes it's not likely to be the half shafts unless I have misunderstood your post.... :scratch:
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sinny
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Post by sinny »

Hi Pete,

Yes changed the pig for a 3.23 & you understood the post I should have said propshaft out of balance!
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